Quantum computing with light
Quantum computers are largely theoretical devices that would exploit the weird properties of matter at extremely small scales to perform calculations, in some cases much more rapidly than conventional computers can. To date, the most promising approach to building quantum computers has been to use ions trapped in electric fields. Using photons — particles of light — instead would have many advantages, but it’s notoriously difficult to get photons to interact: Two photons that collide in a vacuum simply pass through each other.In the Sept. 2 issue of the journal Science, researchers at MIT and Harvard University describe an experiment that allows a single photon to control the quantum state of another photon. The result could have wide-ranging consequences for quantum computing and quantum communication, the quantum analog to conventional telecommunications.A quantum particle has the odd property that it can be in “superposition,” meaning it’s in two different states at...